The present invention relates generally to metering pumps and more specifically to a new design for a metering pump for use in a filling machine.
Pumping units which are used on filling machines generally include five major components, namely a head, a piston, a cylinder, an inlet valve and an outlet valve. The head has an internal chamber connecting the cylinder, inlet valve and outlet valve mounted at appropriate ports. In general, the head has been uniquely designed to receive specific pistons and cylinders, inlet valves and outlet valves. Similarly, the design of the five elements has been dictated by the material to be pumped.
The object of the present metering pump design is to provide ease of disassembly, interchangeable parts, eliminate liquid contact with threads, uniformity of design to reduce the number of parts being inventoried and similarly the cost, as well as the versatility of the system and to improve sealing. A metering pump should be designed to accommodate standard mechanically sealed piston/cylinder assemblies as illustrated in U.S. Pat. No. 2,978,283 as well as sealed piston assemblies as illustrated in U.S. Pat. No. 4,569,378. Although U.S. Pat. No. 2,978,283 shows a readily disassembled metering pump, the seals at the various ports are flat butt seals and their integrity is a function of the pressure brought to bear in the attachment of the inlet and outlet valves and the pump to the head. Similarly, it is noted that the inlet and outlet valves are of different structure.
As discussed in U.S. Pat. No. 3,069,178, the piston rod of the piston pump is received in a closed end cap of the piston's cylinder and requires special sealing or packing to seal the opening while allowing the piston rod to move relative to the cylinder. This is a variation of the usual filling unit which found a limited usage for filling glues, cements and similar products.
The piston rod has been made of two pieces such that the sealing on the Piston head is achieved by compressing the seal between two movable stops of the piston head. This is illustrated specifically in U.S. Pat. No. 2,907,614. This not only increases the number of parts and thereby the cost, but also requires a longer assembly and disassembly time.
The metering pump should be able to interchangeably accommodate the check valves as in U.S. Pat. No. 2,978,283 as well as the spool valve of U.S. Pat. No. 4,055,281. Similarly, it should accommodate duck-bill valves such as those available from Vernay Laboratories, Inc. as well as standard o-ring seals shown in U.S. Pat. Nos. 2,978,149 and 2,978,283. A slightly modified piston head will accommodate the original style "V"-type packing stack.
To increase its versatility, the metering pump should also provide the capability of including a suck-back device. Typical examples of suck-back devices are illustrated in U.S. Pat. Nos. 2,978,149; 3,771,908 and 4,230,160. In each of these devices, the suck-back mechanism requires a modification of the outlet valve, and therefore does not make the structure uniform to that of the inlet valve.
To achieve these and other objects, the head is provided with internal threads terminating adjacent to internal shoulders at each of the pump cylinder port, inlet valve port and outlet valve port. The cylinder, inlet valve and outlet valve each include an external shoulder or flange having a first face which is adjacent to the internal shoulder of the respective port. Preferably, a collar is threadably received in each of the ports and adjacent to the second face of the respective flange for securing the flange to the respective ports. While the head is made of metallic material, the collar is made of non-metallic or other appropriate material to prevent seizure or galling of the connection. This facilitates in the hand disassembly of the structure without the need of tools. O-rings are provided in a circumferential groove in the body or cylinder of the pump inlet valves and outlet valves downstream of or further into the head than the flange. This provides a sealant of the structure which is not dependent on the pressure of the attachment of the cylinder, inlet valve or outlet valve to the head and isolates threads from liquid flow. The flange provided on the cylinder, inlet valve and outlet valve may include a ring extending from a circumferential groove in the body of the pump inlet valve or outlet valve. This permits minor modification of the existing structure without developing new tooling to provide the flange.
A single head design is capable of accommodating both standard mechanically sealed and diaphragm type cylinders, as well as check valves, duck-bill valves and spool valves.
A unique piston pump structure includes a cylinder closed at one end at the pump port by the head. The piston assembly includes a piston rod and a piston head removably mounted at a first end of the piston rod. A bushing is mounted to the piston rod adjacent to the first end of the piston rod. The second end of the cylinder is open. The piston head acts as a first stop for the bushing and a second breakaway stop is connected to the piston rod. The piston head includes a plurality of circumferential grooves for receiving respectively a cup seal, an o-ring seal or self-loading piston packing sets. At least one of the seals is in at least one of the grooves. This allows versatility of sealing design with a single piston head.
The inlet and outlet valves each include an identical first body member having a first valve seat adjacent to its first end and an identical second body member having a second valve seat adjacent to its first end. The first and second body members mate at their second ends and the first end of the first body member is received in the valve port. The inlet and outlet valves each include an identical check valve structure which is positioned in the inlet valve body members to seal on the second seat of the second body member and the check valve structure is positioned in the outlet valve body members to seal on the first valve seat of the first body member. This allows uniformity of the inlet and outlet valve structure to reduce the number of parts. The only difference is the positioning of the check valve structure which could include a ball and a biasing spring or weight or a poppet and spring.
The poppet includes a seal head of a first diameter and a stem of a second diameter smaller than the first diameter extending therefrom. The spring surrounds the stem and extends between the head and a valve seat. The stem has deep grooves defining a low helix along its length so as to rotate the poppet with fluid flowing, thereby cleaning the valve seat. Also the depth of the grooves prevents the stem from closing off the opposing valve seat during high pressure as well as preventing the spring from collapsing sufficiently to cut off the flow.
To incorporate the unique assembly and sealing structure previously discussed, the first body member would have a first flange with a first face adjacent to the internal shoulder of the valve port. The second body member would include a second flange adjacent to the second end of the second body member and having a first face received by the second end of the first body member. A collar is threadably received in the valve port adjacent to the second face of the first and second flanges for securing the first and second flanges to the valve port.
Inlet and outlet valves may also include a spool valve having first and second housing portions received in the inlet and outlet valve ports and a spool therein. The spool includes three components namely, a first and second end spool element separated at their first ends by a third or middle spool element. A connecting rod connects the three spool elements together. First and second circumferential grooves in the second end of the first and second spool elements have seals therein. The third and fourth circumferential grooves are defined between the first end of the first and second spool elements and the third spool element. A seal is also provided in the third and fourth circumferential grooves. Preferably the seal in the first and second circumferential grooves are o-rings whereas the seal in the third and fourth circumferential grooves are cup seals. An air cylinder or driver is mounted to the valve housing and is connected to the spool by a connector or coupling which may be removed without tools. The coupling includes a male and female member which are locked to each other in a coaxial position and are separable at a non-coaxial position.
To maintain uniformity of the body members of the first inlet and outlet valves, the capability of providing a suck-back mechanism is provided in a bore in the head versus the body structure of the outlet valve. The suck-back adjustment includes a stem extending from the exterior of the head into the interior of the head to interact with the outlet valve to adjust the degree of closure of the valve by moving the stem relative to the head. Preferably, the stem includes an eccentric cam which interacts with the valve structure to adjust the degree of closure by rotation of the stem. A locking device is provided to lock the stem with respect to the body after adjustment. An indicator is also provided on the stem, external of the body, for indicating the angular position of the stem.
The suck-back valve structure may be provided in a separate and distinct valve wherein the stem extends through a portion of the body of the valve structure and includes the unique eccentric cam to interact with the valve member to adjust the degree of closure of the valve by rotating the stem. Also, the suck-back valve can be used in the nozzle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.